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Preparation of the Crop Stalk-Based Shaped Activated Carbons and Fibreboard

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Tutor: GaoYanZheng
School: Nanjing Agricultural College
Course: Environmental Science
Keywords: crop stalk,shaping technique,biomass-based activated carbons,polycylic aromatic
CLC: X712
Type: Master's thesis
Year:  2011
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Abstract:
As a renewable resource, crop straw not only rich in carbon, but also can partially replace timber resource. At present, the utilization of straw resource is still limited in china, by way of straw returning, biogas or fertilizer fermented, which is still unable to adequately utilize so larger number of straw. In recent years, researchers recognized that the industrial use was an effective solution to the straw resource. Therefore, developing environmental green high-tech products of crop straw resources such as biomass-based activated carbons and fibreboard has become a research focus. It is not only able to carry out the utilization of agricultural waste, but also to alleviate the shortage of timber resources, with very important theoretical and practical significance.In this work, soybean stalk and straw as crop material was selected to prepare the soybean stalk-based shaped activated carbons and straw fibreboard. The effect of the shaped activated carbons by shaping technique was investigated, and then adsorption effect and mechanism on aqueous PAHs on shaped activated carbons were analyzed. The performance impact of straw fibreboard by different pre-treating was discussed as well. Main novel findings are shown as follows:(1) The BET specific surface and surface morphology of soybean stalk-based shaped activated carbons by different molding technique were dissimilar. The soybean stalk was pyrolyzed at 700¡æin muffle, and then surface modified by H3PO4, the obtained biomass carbons were pressed to obtain the shaped activated carbons by molding technique, and its BET specific surfaces are 320-359 m2¡€g-1, with good pore space structure. The factors that influences the adsorption of the methylene blue follows an descending order:heat treatment temperature> molding pressure> ratio of binder> heat treatment time. The optimum condition obtained the formed biomass activated carbons was binder:15%, molding pressure:65 MPa, heat treatment temperature:260¡æ, and heat treatment time 90 min, respectively. The adsorption value of the methylene blue on shaped activated carbon prepared under these conditions arrived at 135 mg¡€g-1. Shaping technique significantly affected the preparation of the soybean stalk-based shaped activated carbons and adsorption properties of its surface morphology.(2) The soybean stalk-based activated carbons have strong adsorption ability and large adsorption capacity on phenanthrene. They could effectively remove the PAHs in water, and removal efficiencies on phenanthrene were higher than 98%, which is close to commercial activated carbons (CAC). In the experimental concentration range,24 h adsorption isotherms of phenanthrene on the shaped activated carbons were linear (R2>0.97), with partitioning-dominant. Ionic strength significantly affected phenanthrene adsorption on the shaped activated carbons, with ionic strength increased; the adsorption capacity and adsorption rate were gradually decreased. Owing to the difference in the pore structure (pore shape, pore size and pore distribution) and molecular polarity, partition coefficient, and water solubility of pollutants and so on, the removal abilities under composite pollution of the shaped activated carbons were different. The removal ability to three PAHs of the shaped activated carbons follows an descending order:phenanthrene> naphthalene> acenaphthene. And for the shaped activated carbons basing on different treatments, there is an obvious discrepancy in PAHs absorption.(3) Hydrothermal treatment temperature and time could evidently affected the mechanical properties of straw fibreboard. At the range of 40¡«100¡æ, with temperature increased, the mechanical properties of fibreboard augmented significantly. However, with time prolonged, the mechanical properties of fibreboard increased firstly, and then decreased. The optimum condition of hydrothermal treatment was temperature 100¡æfor time 20 min.Moderate increase of resin content could improve the mechanical properties of fibreboard and excessive resin just only increased the layer thickness on the fibreboard, but it couldn¡¯t play a positive role in the mechanical properties of fibreboard. The optimum condition of resin content is 12%. Acetic acid treatment could deeply change the surface properties of straw fiber, and provide a good bonding environment to enhance the mechanical properties of fibreboard. The optimum condition of acetic acid treatment was resin content 4%, temperature 80¡æand time 20 min.
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