热解温度对生物炭物理及化学吸附能力的影响

Effect of Pyrolysis Temperature on Physical and Chemical Adsorption Capacity of Biochar

为明确生物炭物理及化学吸附能力对热解温度的响应特征,并阐明生物炭物理、化学吸附能力与热解温度的量化关系,试验以农林废弃树枝为原料,在热解温度为250、350、450、550、650℃下制备具不同吸附性能的生物炭(以T250、T350、T450、T550、T650命名),测定生物炭碘吸附量(表征物理吸附能力)、亚甲基蓝吸附量(表征化学吸附能力)、芳香性、极性,并利用扫描电镜(SEM)、傅里叶红外光谱(FTIR)对生物炭表观形貌及官能团丰富度进行分析。结果表明:热解温度的升高,提高了生物炭的碘吸附量、降低了生物炭的亚甲基蓝吸附量,T250、T350处理的生物炭表面具有较丰富的含氧官能团,而T450、T550、T650处理的生物炭则拥有更强的芳香性、更低的极性和更加丰富的孔隙结构;生物炭碘吸附量Q_(2)与热解温度x呈增长型“S”曲线关系(P<0.01),回归方程为:Q_(1)=180.78+(447.96-180.78)/[1+10^(484.61-x)0.02],R^(2)=0.9991,碘吸附量的极小值、中值、极大值所对应的热解温度分别为318.1、484.6、616.4℃;生物炭亚甲基蓝吸附量Q_(2)与热解温度x呈下降型“S”曲线关系(P<0.01),回归方程为:Q_(2)=5.78+(12.45-5.78)/[1+10^(386.78-x)-0.02],R^(2)=0.9920,亚甲基蓝吸附量的极小值、中值、极大值所对应的热解温度分别为511.3、386.8、281.6℃;热解温度每升高50℃生物炭的碘吸附量提高16.7%、亚甲基蓝吸附量降低21.8%。综合吸附原理及特征参数,在不同生产实践场景中,若主要应用以化学吸附作用为主的生物炭,其热解温度推荐值不宜高于386.8℃;若重点发挥生物炭的物理吸附作用,热解温度推荐值不宜低于484.6℃。热解温度介于386.8~484.6℃之间,生物炭物理与化学吸附能力无显著的主次之分。

To elucidate the response characteristics of biochar’s physical and chemical adsorption capacities to pyrolysis temperature and to clarify the quantitative relationship between biochar’s adsorption capabilities and pyrolysis temperature,we carried out the following experiment.In this experiment,biochar samples with different properties were prepared from agricultural and forestry waste branches at five pyrolysis temperatures(250,350,450,550 and 650℃).Each treatment was named T250,T350,T450,T550 and T650,respectively.In this experiment,the physical and chemical adsorption capacity of biochar was reflected by measuring the iodine adsorption capacity and methylene blue adsorption capacity of biochar.Additionally,the aromaticity and polarity of biochar were determined,and the apparent morphology and functional group richness of biochar were analyzed by scanning electron microscopy(SEM)and Fourier-transform infrared spectroscopy(FTIR).The results indicated that the increase of pyrolysis temperature enhanced the biochar’s iodine adsorption capacity while decreased its methylene blue adsorption capacity.The T250 and T350 treatment had abundant oxygen-containing functional groups,while the biochar treated with T450,T550 and T650 had stronger aromaticity,lower polarity and richer pore structure.The relationship between biochar’s iodine adsorption capacity(Q1)and pyrolysis temperature(x)conformed to the growth“S”curve,specifically:Q_(1)=180.78+(447.96-180.78)/[1+10^(484.61-x)0.02],R^(2)=0.9991.The minimum,median and maximum values of biochar’s iodine adsorption capacity correspond to pyrolysis temperatures was 318.1,484.6 and 616.4℃,respectively.The relationship between methylene blue adsorption capacity(Q_(2))and pyrolysis temperature(x)of biochar conformed to the decreasing“S”curve,specifically(P<0.01):Q_(2)=5.78+(12.45-5.78)/[1+10^(386.78-x)-0.02],R^(2)=0.9920.The minimum,median and maximum values of biochar’s methylene blue adsorption capacity correspond to pyrolysis temperatures was 511.3,386.8 and 284.6℃,respectively.For every 50℃increase in pyrolysis temperature,the average iodine adsorption capacity of biochar increased by 16.7%,while the average methylene blue adsorption capacity decreased by 21.8%.Considering the adsorption principles and characteristic parameters,in different practical production scenarios,if the main application was chemical adsorption-based biochar,the recommended pyrolysis temperature should not exceed 386.8℃.If the focus was on biochar’s physical adsorption function,the recommended pyrolysis temperature should not be lower than 484.6℃.When the pyrolysis temperature is between 386.8 and 484.6℃,there was no significant distinction between the physical and chemical adsorption capabilities of biochar.