Preparation, Characterization And Application Of Porous Materials Derived From Pyrolyzed Rice Husk

High value-added utilization of char from biomass pyrolysis is a key factor for industrialization of fast pyrolyzing biomass, a promising technique for efficient conversion of biomass into a liquid product known as biooil. Fast pyrolyzed rice husk (PRH) is a typical char produced by fast pyrolyzing biomass, but currently few researches have been conducted on high value-added utilization of PRH. This study aims to prepare active carbon and porous silica from PRH. The main research and innovative results can be divided into four aspects. (1) A novel process, namely combination of CO₂ activation and boiling in alkaline solution under normal pressure, was proposed to efficiently utilize PRH. By using this process, active carbons with mesopore fraction up to 79% and 50% can be prepared without requiring inorganic alkali to undergo high temperature treatment or consume a large amount of alkali. The process also allows producing sodium silicate or porous silica. (2) The adsorption of methylene blue (MB) onto the active carbons with different mesopore fraction was studied. (3) Porous silica with specific surface area (SSA) up to 1018 m2/g was produced within 10 h by using polyethylene glycol (PEG) as a template and H3PO4 as a acidulant. (4) The adsorption of Cu(â…¡) onto porous silica prepared from PRH was studied for the first time. More detailed research contents were given as follows.1 Preparation of PRH-based active carbon with high mesopore fraction by combination of CO₂ activation and boiling in alkaline solution under normal pressure.A new process, namely combination of activating carbonized PRH with CO₂ and then boiling it in alkaline solution under normal pressure, was proposed to prepare active carbon. Effects of process variables on iodine number of active carbons were studied using an orthogonal experimental design, followed by discussion on pore development mechanism. The results indicated that by using the proposed research, PRH-based active carbon with mesopore fraction, pore volume and SSA up to 79%, 0.783 cm³/g and 899 m²/g can be successfully produced without requiring inorganic alkali to undergo high temperature treatment or consume a large amount of alkali. The effect of CO₂ activation time on iodine number was more significant than any other process variable studied. The pore development of active carbons can be attributed to initial pore development resulting from removal of carbon from the precursor by CO₂ activation, and further pore development caused by dissolution of silica in alkaline solution. 2 Co-production of sodium silicate and active carbon from PRHTo produce sodium silicate with large silica content and high modulus, and active carbons with SSA higher than 800 m²/g under normal pressure by using a small quantity of alkali, the proposed process was optimized by using Doehlert experimental design, Derringer desirability function and surface response model. The optimum co-production condition was found to be using 1 mol/L NaOH solution and 9.7 mL/g liquid-solid ratio, under which sodium silicate with modulus reaching 2.6, and active carbon with 897 m²/g SSA and 50% mesopore fraction can be manufactured. The adsorption quantities of phenol and Ni²⁺ by the active carbon were both significantly higher than the corresponding values of excellent commercial active carbon.3 Adsorption characteristics of MB onto PHR-based active carbon with different mesopore fractionThe adsorption characteristics of MB onto PHR-based active carbon with different mesopore fraction were studied using batch adsorption experiments. The results showed that the MB adsorption amounts of the two active carbons were both comparable to that of excellent commercial active carbon at intial MB concentration not larger than 280 mg/L. The removal efficiency of the two active carbons was both higher than 86% at initial MB concentration of 310-380 mg/L.4 Short-period production of high SSA silica from PRHPorous silica was prepared from the sodium silicate produced under the optimum co-production condition by using PEG as a template. Effects of PEG dosage and pH on the textural properties of porous silica were investigated, including the mechanism of the effects. The results showed that PRH-based porous silica with SSA ranging from 709 m²/g to 1018 m²/g was prepared with 10h. Increasing the PEG dosage or reducing pH can significantly enhance the SSA of porous silica. The reason was that more PEG was incorporated into the PEG-silica composites when the PEG dosage increased or the pH decreased, and hence more pores were created after PEG was removed from the composites.5 Adsorption characteristics of Cu(â…¡)onto PRH-based porous silicaThe adsorption characteristics of Cu(â…¡)onto PRH-based porous silica was studied by batch adsorption experiments after characterization of the adsorbent. The largest adsorption capacity and highest removal efficiency for Cu(â…¡)at initial Cu(â…¡) concentrations of 20-120 mg/L were 77 mg/g and 97 %, respectively. The adsorption of Cu(â…¡) onto the silica could be described by the Freundlich isotherm and the pseudo-second-order model. Interaction of silanol group on porous silica surface with Cu(â…¡)was an important reason for adsorption of Cu(â…¡).