热解温度对花生壳生物质炭吸附去除水中4-硝基酚的影响

    Adsorption-remove effect of p-nitrophenol in water by peanut shell biochar at different pyrolysis temperatures

    • 摘要: 为提升农业废弃物的资源化再利用价值,以花生壳为原料,在不同热解温度(400、500、600 ℃)下限氧制备花生壳生物质炭(BC400、BC500、BC600),考察其对水中4-硝基酚的吸附效果。生物质炭表面灰分通过酸洗法去除,采用批量吸附试验的方法分析生物质炭对PNP吸附特性的影响,并结合元素分析、扫描电镜及红外光谱图方法,探讨热解温度对生物质炭吸附水中PNP特性的影响。结果表明,生物质炭总产量随温度升高而降低,其含碳量随温度升高逐渐增加;生物质炭中含氧官能团随温度的升高而减少,芳香性增强,有利于对有机物的吸附。吸附等温线符合Freundlich模型,线性拟合很好,R2在0.954~0.991之间;对比伪二级动力学模型、Elovich模型、颗粒内扩散模型可知,吸附过程与伪二级吸附动力学模型拟合效果最佳,R2在0.981~0.999之间,平衡吸附量随热解温度升高而增大,BC600>BC500>BC400,BC600的吸附容量为34.48 mg/g,是BC400的2.25倍。以NaOH为解吸剂,当NaOH质量浓度为1.0 mg/L时对4-硝基酚的解吸效率最高,为68.21%,可见生物质炭的再生利用具有一定的可行性。因此,高温制备的花生壳生物质炭可作为去除4-硝基酚的良好功能材料。

       

      Abstract: Biomass carbon is produced from wood or other agricultural and forestry wastes by high temperature pyrolysis under low oxygen or oxygen-limited conditions. It has high carbon content and porosity, large specific surface area and good adsorption performance. In addition, the preparation process is simple and the materials are widely available. Peanut is an important oil crop in China, thus peanut shell is a kind of agricultural waste with a large output. The comprehensive utilization value of peanut shell has been widely concerned. Therefore, biomass carbon has received extensive attention in soil remediation, sewage and waste gas treatment. The adsorption of p-nitrophenol (PNP) by biochars (BC400, BC500, BC600) prepared from pyrolysis of peanut shells at different temperature (400, 500, 600 ℃) was investigated by batch adsorption experiments. The amount of biomass charcoal produced at different temperature conditions decreased from 28.83% at 400 ℃ to 19.40% at 600 ℃. The pyrolysis reaction of biomass charcoal at 400-500 ℃ was more severe than that at 500-600 ℃, and the mass loss ratio was decreased from 42.3% to 31.1%; The ash and volatile matter increased significantly with the increase of pyrolysis temperature, while the water content showed a slow downward trend. The ash on the surface of biochar was removed by hydrochloric acid washing. Combined with the element analysis, scanning electron microscope (SEM), and Fourier transform infrared spectroscopy (FTIR) analysis method, pyrolysis temperature showed a pronounced effect on properties of biochar, so effecting its adsorption characteristics on PNP. The deoxidation and dehydrogenation reaction of peanut shells in the process of pyrolysis and carbonization increased with the increase of temperature, and the degree of carbonization increased with the increase of temperature. At the same time, the ratio of biomass carbon H/C, O/C, (O+N)/C gradually decreased, reflecting that the oxygen-containing functional groups in biomass carbon decreased with the increasing temperature. The biomass carbon with more complete aromatic structure had stronger hydrophobicity and lower polarity, which was beneficial to increase the adsorption capacity of biomass carbon for organic matter. Results showed that the output of biochar was decreased with rise of temperature, but the carbon content gradually increased, reflecting that the functional groups containing oxygen in the biochar decreased with the rise of temperature. The higher temperature of pyrolysis was, the more stability of the biochar structure. Adsorption isotherm conformed with the Freundlich model, linear fitting was very good, R2 was between 0.954-0.991. Contrasting pseudo secondary dynamics model, the Elovich model and the diffusion model in particle adsorption behavior, the results showed that the pseudo secondary adsorption dynamics model fitting effect was best, R2 was between 0.981-0.999, equilibrium adsorption amount increased with the rise of the biochar preparation temperature (BC600> BC500>BC400). BC600 adsorption capacity was 34.48 mg/g, that was 2.25 times of the BC400. With NaOH as desorbent, the desorption efficiency of PNP was the highest at 68.21% when the concentration of NaOH was 1.0 mg/L. It can be seen that the regeneration of biomass carbon had certain feasibility. Therefore, the preparation of high temperature peanut shells biochar can be used as a good functional material for PNP removal. Peanut shell biomass carbon has broad development prospects in the field of sewage treatment.

       

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