K_(2)CO_(3)催化热解棉秆及其含钾半焦产物对焦油的催化降解

Catalytic Pyrolysis of Cotton Stalk by K_(2)CO_(3) and Its Potassium-Containing Semi-Coke Products Used for Catalytic Degradation of Tar

生物质热解过程中产生的焦油对设备和环境造成严重危害,探究K_(2)CO_(3)催化棉秆热解生成焦油的影响机制以及含钾半焦对焦油的催化降解作用,对实现生物质能源高效利用具有重要意义。本工作在600℃条件下,采用卧式固定床催化热解实验装置研究棉秆的催化热解特性。结果表明:添加K_(2)CO_(3)能抑制焦油产生,K_(2)CO_(3)添加量为7.5%(质量分数)时,焦油产率由未添加K_(2)CO_(3)时的43%降至33%,且焦油中芳香烃含量增大。基于密度泛函理论的半纤维素模型化合物4-O-甲基葡萄糖醛酸的分子热解计算结果表明,钾活化了4-O-甲基葡萄糖醛酸侧链基团,使—OH更易于脱除。进一步以甲苯作为焦油的模型化合物,开展棉秆半焦异相降解甲苯实验研究,发现添加K_(2)CO_(3)使热解半焦的比表面积增大、半焦表面吸附位点增多,增强了甲苯的降解缩合反应。可见,添加K_(2)CO_(3)能在热解初始阶段减少焦油产生,同时回收含钾半焦作为催化剂能够强化焦油降解,为提高棉秆资源利用率提供了新思路。

Tar produced during biomass pyrolysis has caused serious harm to equipment and environment.Exploring the influence mechanism of K_(2)CO_(3) catalytic pyrolysis of cotton stalk to generate tar and the catalytic degradation of tar by potassium-containing semi-coke is of great significance for realizing efficient utilization of biomass energy.In this work,the catalytic pyrolysis characteristics of cotton stalk were studied with a horizontal fixed bed catalytic pyrolysis experimental device at 600℃.The results showed that the addition of K_(2)CO_(3) could inhibit tar production.When the addition of K_(2)CO_(3) was 7.5%(mass fraction),the tar yield decreased from 43%to 33%(without K_(2)CO_(3)),and the content of aromatic hydrocarbons in tar increased.The molecular pyrolysis results of the hemicellulose model compound 4-O-methylglucuronic acid based on density functional theory show that potassium activates the side chain groups of 4-O-methylglucuronic acid,which makes it easier to remove-OH.Using toluene as the model compound of tar,the heterogeneous degradation of toluene by cotton straw semi-coke was studied.It was found that the addition of K_(2)CO_(3) increased the specific surface area and adsorption sites on the semi-coke surface,which enhanced the degradation and condensation reaction of toluene.In conclusion,the addition of K_(2)CO_(3) can reduce tar production at the initial stage of pyrolysis,and the recovery of potassium-containing semi-coke as a catalyst can strengthen tar degradation,providing a new idea for improving the utilization rate of cotton stalk resources.