碳酸钾活化剂法制备稻壳活性炭的工艺优化

为实现农业废弃物的资源化利用,该文以稻壳为原料、K2CO3为活化剂制备稻壳基活性炭。采用Plackett-Burman(P-B)和中心复合设计(central composite design,CCD)法对影响稻壳基活性炭得率和碘吸附性能的5个工艺因素进行筛选和优化,确定样品得率和碘吸附值的预测模型,并进行验证。结果表明,所建立的稻壳基活性炭得率和碘吸附值回归方程的决定系数R2分别为0.90和0.85,影响样品得率的主要因素为:活化温度活化时间K2CO3浓度,影响样品碘吸附值的主要因素为:活化温度K2CO3浓度活化时间,浸渍体积比和浸渍时间影响不显著;经CCD法建立的稻壳基活性炭得率和碘吸附值的预测模型极显著(P0.0001,P0.01),决定系数R2可达0.92和0.90,活化温度和活化时间之间存在较强的交互作用。优化后的工艺条件为:活化温度1029.17 K、K2CO3浓度1.95 mo L/L、活化时间1.17 h、浸渍体积比3,浸渍时间11 h,其得率和碘吸附值的预测值分别为13.61%、1058.83 mg/g,与实测值(14.53%、1021.30mg/g)的误差仅为6.33%、3.67%,拟合性良好,说明运用CCD法对稻壳基活性炭制备工艺的优化是准确可靠的。该结果可为K2CO3活化法制备稻壳基活性炭的工业化生产提供一定的参考。

Optimizing preparation of activated carbons from rice husk by K2CO3 chemical activation

Abstract: The purpose of the present study was to realize the resource utilization of agricultural byproduct. In this paper, we used rice husk as materials for producing activated carbon. Five factors which affected the yield and iodine absorption performance of rice husk-based activated carbon were sifted and optimized by Plackett-Burman (P-B) and Central Composite Design (CCD). Based on those, the prediction models of yield and iodine adsorption rate were determined and validated. The measurement of iodine absorption rate was based on the method of the GB/T 12,496.1-12,496.22-1999. The results showed that the determination coefficients (R2) of regression equations which established for the yield and iodine adsorption rate of activated carbon samples were 0.90 and 0.85, respectively. The first main factor which influenced the yield of activated carbon was activation temperature followed by activation time and concentration of K2CO3. For the iodine adsorption rate of activated carbon, activation temperature still played an important role in the preparation process, and the next were the concentration of K2CO3 and activation time. The impregnation volume ratio and impregnation time had little influence on the performance of rice husk-based activated carbon. The prediction models which were established by the CCD had a highly significant correlation (P<0.0001) and the determination coefficients (R2) reached 0.92 and 0.90, respectively. There was a strong interaction between the activation temperature and activation time. The response surface analysis indicated that when the activation time was at the center value of 0.92 h and the concentration of K2CO3 remained a constant, the iodine adsorption rate increased with the rise of activation temperature. It can be well illustrated that high activation temperature can promote the chemical reaction. However, the iodine adsorption rate decreased with the extension of activation time when the concentration of K2CO3 was at the center value of 1.5 mol/L and activation temperature remained a constant. This was because that long activation time made the micropore of samples sintered, thus it affected the adsorption performance of rice husk-based activated carbon. With the increased concentration of K2CO3, the iodine adsorption rate showed a gradually increasing trend when the activation temperature was at the center value of 1098 K and activation time remained a constant. It was the reason that more active agent can increase the contact area, which accelerated the reaction distinctively. The optimal conditions were that the rice husk was infused in the K2CO3 solution with concentration and impregnation volume ratio (K2CO3/rice husk) of 1.95 mol/L and 3, respectively after impregnating for 11 h, they were heated for 1.17 h at 1173 K. The prediction value of yield and iodine adsorption rate were 13.61%, 1058.83 mg/g, and the adequacy of the model equation for predicting the optimum response values was verified effectively by the experiment, and the experimental values (14.53%, 1021.30 mg/g) agreed with the predicted values of the model equation with 6.33%, 3.67% deviation, respectively. Our results indicated that optimizing the preparation of rice husk-based activated carbon by using CCD was reliable. This study can provide an important reference for the preparation of activated carbons from rice husk in the industrial production.