微波诱导热解制备小麦秸秆吸附剂及响应面优化工艺研究

Approach tooptimizing process of wheat-straw adsorbent through microwave pyrolysis with surface response method

以氯化锌为活化剂,通过微波诱导热解法制备小麦秸秆吸附剂,并以微波功率、热解时间和氯化锌质量分数为影响因素,碘吸附值为响应值,采用响应面法对小麦秸秆吸附剂的制备工艺进行优化。结果表明,热解时间和微波功率对碘吸附值的交互作用明显。响应面优化工艺分析,发现当热解时间4.03 min、微波功率569.0 W,氯化锌质量分数为31.24%时,碘吸附值最大,为643.33 mg/g。另外,小麦秸秆吸附等温线与I型相似,吸附剂的微孔容积为0.238 4cm^(3)/g,吸附剂的BJH孔径分布表现窄小,最高峰出现在2.1nm左右。处理Cr(VI)废水的吸附试验,发现Cr(VI)的去除率可以达到70%以上。研究表明,微波诱导热解法及响应面优化工艺制备的小麦秸秆吸附剂技术可行且具有良好的重金属废水处理应用前景。

The paper is aimed to improve the agricultural waste resourceful utilization through investigating the effective preparation method for wheat straw application. For the said research purpose,we have proposed a microwave induced pyrolysis for the farming waste adsorbent derived from the wheat straw with zinc chloride as an active agent. The exact process can be illustrated as follows: taking the iodine as the response agent on the basis of Box-Behnken response surface methodology,it would be optimistic that the manufacture process of wheat straw adsorbent can be realized with the microwave power,the pyrolysis time,and the zinc chloride concentration as the response variables. The experimental results suggest that the pyrolysis time and the microwave power can have a significant positive reaction to the iodine indexes,though there doesn’t exist any pronounced interactive effect existing between the pyrolysis time(and microwave power) and the zinc chloride mass fraction. What is more,it can be confirmed that the optimization process of the response surface can help to provide optimistic conditions as follows: a pyrolysis time of 4. 03 min,a microwave power of 569. 0 W,and a zinc chloride concentration of 31. 24%,with the maximum iodine value of the wheat straw adsorbent being 643. 33 mg/g. The actual nitrogen adsorption and desorption isotherms from the wheat straw have shown that the adsorption isotherm of the adsorbent tends to be Type I adsorption ruled by the International Union of Pure and Applied Chemistry( IUPAC) standard. The adsorption process of wheat straws can also be found well represented by the monolayer adsorption process of Langmuir isotherm model when it occurs mainly within the micropores. On the other hand,the measured pressure signals can also be observed in the state of increase,which proves that the adsorption and desorption isotherms of the wheat straw do not seem to be coincided with each other. Therefore,there ought to be presumably some slits that can be produced by the surface structure of the wheat straw. The nitrogen adsorption results help us to find that the micropore volume is actually 0. 238 4 cm3/g. The curve of BJH can thus be characterized as the narrow pore size distribution with the pore size being peaked at about 2. 1 nm. Furthermore,the prepared wheat straw adsorbent can be expectantly used to treat the chromium-content sewage mentioned above in this paper,whose removal efficiency of chromium VI by the adsorbent can be so high as beyond 70%. Therefore,the wheat straw adsorbent by the microwave pyrolysis with response surface optimization methodology is technically feasible with the perfect efficiency in heavy metal sewage disposal.