The effect of type pulping process on the desilication of rice straw black liquor

Rice straw in the countries without adequate woody lignocellulosic materials can be used as one of the suitable raw materials for the production of chemical pulp. But silica present in the straw causes limitations for its use in this industry and adversely affects sections such as: the raw material preparation، digester، chemical recovery system، recausticizing and paper machine as well as recovery of sodium and energy. In this study، effect of different pulping process such as soda، soda-AQ and formic acid on the desilication of rice straw black liquor at three kappa number 15، 25 and 35 has been studied. The results have shown that in soda pulping process with increasing of chemical charge and consequently kappa number decreasing from 35 to 15 led to reduction of silica deposition in the pulp from 17. 3 to 7. 4 percent while silica content in black liquor increased from 1. 34 to 11. 2 percent. The amount of silica in soda-AQ black liquor pulping was lower in comparison with soda pulping process in about 115%. The results in formic acid pulping were significantly different from mentioned conventional pulping and it indicated that silica content of pulp is increased with decreasing of kappa number from 35 to 15. So that pulp silica content at kappa number 15 was 18%. Therefore in the case of using soda-AQ and formic acid pulping of rice straw not only significant reduction of silica in the black liquor may be obtained but also production of chemical pulp without any environmental problems can more be economical.